&xmppcore; describes the client-server architecture upon which Jabber/XMPP communication is based. One aspect of such communication is "federation", i.e., the ability for two XMPP servers in different domains to exchange XML stanzas. There are at least four levels of federation:

Permissive Federation -- a server accepts a connection from any other peer on the network, even without verifiying the identity of the peer based on DNS lookups. The lack of peer verification or authentication means that domains can be spoofed. Permissive federation was effectively outlawed on the Jabber network in October 2000 with the release of the jabberd 1.2 server, which included support for the newly-developed &xep0220; protocol.

Verified Federation -- a server accepts a connection from a peer only after the identity of the peer has been weakly verified via Server Dialback, based on information obtained via the Domain Name System (DNS) and verification keys exchanged in-band over XMPP. However, the connection is not encrypted. The use of identity verification effectively prevents domain spoofing, but federation requires proper DNS setup and is still subject to DNS poisoning attacks. Verified federation has been the default service policy followed by servers on the open XMPP network from October 2000 until now.

Encrypted Federation -- a server accepts a connection from a peer only if the peer supports Transport Layer Security (TLS) as defined for XMPP in &xmppcore; and the peer presents a digital certificate. However, the certificate may be self-signed, in which case mutual authentication is typically not possible. Therefore, after STARTTLS negotiation the parties proceed to weakly verify identity using Server Dialback. This combination results in an encrypted connection with weak identity verification.

Trusted Federation -- a server accepts a connection from a peer only if the peer supports Transport Layer Security (TLS) and the peer presents a digital certificate issued by a trusted root certification authority (CA). The list of trusted root CAs is determined by local service policy, as is the level of trust accorded to various types of certificates (i.e., Class 1, Class 2, or Class 3). The use of trusted domain certificates effectively prevents DNS poisoning attacks but makes federation more difficult since typically such certificates are not easy to obtain.

The remainder of this document describes in more detail the protocol flows that make it possible to deploy verified federation, encrypted federation, and trusted federation. Protocol flows are shown for federation attempts between various combinations to illustrate the interaction between different federation policies.

To simplify the text, this document uses the following terminology. For each service type, the domain "example.lit" is used to illustrate connections to that same service type.

Service Type

Federation Policy

Certificate

Protocols Supported

Example Domain

Example User

Type 1

Verified Only

None

XMPP 0.9 "XMPP 0.9" is the core XML streaming protocol used in the Jabber community before the formalization of XMPP 1.0 by the IETF in &rfc3920;, including STARTTLS and SASL. and Server Dialback

type1.lit

citizen@type1.lit

Type 2

Verified Acceptable

Self-signed

XMPP 1.0 "XMPP 1.0" is defined in RFC 3920 and includes STARTTLS and SASL negotiation. and Server Dialback

type2.lit

juliet@type2.lit

Type 3

Verified Acceptable

CA-issued

XMPP 1.0 and Server Dialback

type3.lit

romeo@type3.lit

Type 4

Encrypted Required

Self-signed

XMPP 1.0 and Server Dialback

type4.lit

hamlet@type4.lit

Type 5

Encrypted Required

CA-issued

XMPP 1.0 and Server Dialback

type5.lit

bill@type5.lit

Type 6

Trusted Required

CA-issued

XMPP 1.0

type6.lit

chris@type6.lit

The following table summarizes the results of connection attempts between the various services, where "U" stands for "Unsuccessful", "V" stands for "Verified", "E" stands for "Encrypted", and "T" stands for "Trusted". The rows indicate the initiating service and the columns indicate the receiving service.

Type 1

Type 2

Type 3

Type 4

Type 5

Type 6

Type 1

V

V

V

U

U

U

Type 2

V

V

E

E

U

U

Type 3

V

V

E

E

E

T

Type 4

U

E

E

E

E

U

Type 5

U

E

T

E

T

T

Type 6

U

U

T

U

T

T

In this scenario, an XMPP user citizen@type1.lit attempts to send an XML stanza to user@example.lit.

]]>

Therefore the type1.lit service attempts to initiate a server-to-server connection with example.lit (both of which support verified connections only and neither of which has a certificate).

First, the type1.lit service sends an initial stream header to example.lit.

]]>

Next the example.lit service sends a response stream header to type1.lit.

]]>

Because neither service supports XMPP 1.0, the type1.lit service attempts to complete a server dialback negotiation with the example.lit service. Therefore it sends a dialback key to example.lit over the existing connection.

some-long-dialback-key
]]>

The example.lit service then performs a DNS lookup on the type1.lit domain, opens a TCP connection at the discovered IP address and port, and establishes a stream with the authoritative server for the type1.lit service.

]]>

The authoritative server for the type1.lit service then returns a response stream header.

]]>

The example.lit service then sends a dialback verification request to the authoritative server for the type1.lit domain.

some-long-dialback-key
]]>

Here we assume that the authoritative server for the type1.lit domain notifies the example.lit service that the key is valid.

some-long-dialback-key
]]>

The example.lit service then returns a positive server dialback result to the originating server.

some-long-dialback-key
]]>

Because the connection is successful, the type1.lit service routes the XML stanza from citizen@type1.lit to the example.lit service.

In this scenario, an XMPP user citizen@type1.lit attempts to send an XML stanza to juliet@type2.lit:

]]>

Therefore the type1.lit service (which supports verified connections only and does not have a certificate) attempts to initiate a server-to-server connection with the type2.lit service (which accepts verified connections and has a self-signed certificate).

First, the type1.lit service sends an initial stream header to type2.lit.

]]>

Next the type2.lit service sends a response stream header to type1.lit.

]]>

The type2.lit service also sends stream features.

]]>

Because the type1.lit service does not support XMPP 1.0, it ignores the stream features and attempts to complete a server dialback negotiation with the type2.lit service. Therefore it sends a dialback key to type2.lit over the existing connection.

some-long-dialback-key
]]>

The type2.lit service then performs a DNS lookup on the type1.lit domain, opens a TCP connection at the discovered IP address and port, and establishes a stream with the authoritative server for the type1.lit service.

]]>

The authoritative server for the type1.lit service then returns a response stream header.

]]>

The type2.lit service then sends a dialback verification request to the authoritative server for the type1.lit domain.

some-long-dialback-key
]]>

Here we assume that the authoritative server for the type1.lit domain notifies the type2.lit service that the key is valid.

some-long-dialback-key
]]>

The type2.lit service then returns a positive server dialback result to the originating server.

some-long-dialback-key
]]>

Because the connection is successful, the type1.lit service routes the XML stanza from citizen@type1.lit to the type2.lit service.

In this scenario, an XMPP user citizen@type1.lit attempts to send an XML stanza to romeo@type3.lit.

]]>

Therefore the type1.lit service (which supports verified connections only and does not have a certificate) attempts to initiate a server-to-server connection with the type3.lit service (which accepts verified connections and has a CA-issued certificate).

First, the type1.lit service sends an initial stream header to type3.lit.

]]>

Next the type3.lit service sends a response stream header to type1.lit.

]]>

The type3.lit service also sends stream features.

]]>

Because the type1.lit service does not support XMPP 1.0, it ignores the stream features and attempts to complete a server dialback negotiation with the type3.lit service. Therefore it sends a dialback key to the authoritative server for the type3.lit service.

some-long-dialback-key
]]>

The type3.lit service then performs a DNS lookup on the type1.lit domain, opens a TCP connection at the discovered IP address and port, and establishes a stream with the authoritative server.

]]>

The authoritative server for the type1.lit service then returns a response stream header.

]]>

The type3.lit service then sends a dialback verification request to the authoritative server for the type1.lit domain.

some-long-dialback-key
]]>

Here we assume that the authoritative server for the type1.lit domain notifies the type3.lit service that the key is valid.

some-long-dialback-key
]]>

The type3.lit service then returns a positive server dialback result to the originating server.

some-long-dialback-key
]]>

Because the connection is successful, the type1.lit service routes the XML stanza from citizen@type1.lit to the type3.lit service.

In this scenario, an XMPP user citizen@type1.lit attempts to send an XML stanza to hamlet@type4.lit.

]]>

Therefore the type1.lit service (which supports verified connections only and does not have a certificate) attempts to initiate a server-to-server connection with type4.lit (which does not accept verified connections and has a self-signed certificate).

First, the type1.lit service sends an initial stream header to type4.lit.

]]>

Next the type4.lit service sends a response stream header to type1.lit.

]]>

The type4.lit service also sends stream features. Because the type4.lit service does not accept verified connections, it returns stream features with a notation that STARTTLS is required.

]]>

Because the type1.lit service does not support XMPP 1.0, it ignores the stream features and attempts to complete a server dialback negotiation with the type4.lit service. Therefore it sends a dialback key to the authoritative server for the type4.lit service.

some-long-dialback-key
]]>

The type4.lit service understands the server dialback protocol but since it requires STARTTLS at this point in the stream negotiation it returns a stream error to the type1.lit service, which should be <not-authorized/>.

]]>

Because the connection is unsuccessful, the type1.lit service returns a stanza error to citizen@type1.lit, which should be &timeout;.

]]>

In this scenario, an XMPP user citizen@type1.lit attempts to send an XML stanza to bill@type5.lit.

]]>

Therefore the type1.lit service (which supports verified connections only and does not have a certificate) attempts to initiate a server-to-server connection with type5.lit (which does not accept verified connections and has a CA-issued signed certificate).

First, the type1.lit service sends an initial stream header to type5.lit.

]]>

Next the type5.lit service sends a response stream header to type1.lit.

]]>

The type5.lit service also sends stream features. Because the type5.lit service does not accept verified connections, it returns stream features with a notation that STARTTLS is required.

]]>

Because the type1.lit service does not support XMPP 1.0, it ignores the stream features and attempts to complete a server dialback negotiation with the type5.lit service. Therefore it sends a dialback key to the authoritative server for the type5.lit service.

some-long-dialback-key
]]>

The type5.lit service understands the server dialback protocol but since it requires STARTTLS at this point in the stream negotiation it returns a stream error to the type1.lit service, which should be <not-authorized/>.

]]>

Because the connection is unsuccessful, the type1.lit service returns a stanza error to citizen@type1.lit, which should be &timeout;.

]]>

In this scenario, an XMPP user citizen@type1.lit attempts to send an XML stanza to chris@type6.lit.

]]>

Therefore the type1.lit service (which supports verified connections only and does not have a certificate) attempts to initiate a server-to-server connection with the type6.lit service (which accepts only trusted connections, has a CA-issued certificate, and does not support Server Dialback).

First, the type1.lit service sends an initial stream header to type6.lit.

]]>

Next the type6.lit service sends a response stream header to type1.lit. Notice that the response stream header does not include the dialback namespace, since the type6.lit service does not support Server Dialback.

]]>

The type6.lit service also sends stream features. Because the type6.lit service does not accept untrusted connections, it returns stream features with a notation that STARTTLS is required.

]]>

The type1.lit service does not detect support for server dialback by the type6.lit service but in any case attempts to complete server dialback.

some-long-dialback-key
]]>

The type6.lit service does not accept dialback negotiations so it returns a &notauthorized; stream error and closes the stream.

]]>

The type1.lit service closes the stream as well.

]]>

Because the connection is unsuccessful, the type1.lit service returns a stanza error to citizen@type1.lit, which should be &timeout;.

]]>

In this scenario, an XMPP user juliet@type2.lit attempts to send an XML stanza to citizen@type1.lit:

]]>

Therefore the type2.lit service (which accepts verified connections and has a self-signed certificate) attempts to initiate a server-to-server connection with the type1.lit service (which supports verified connections only and does not have a certificate).

First, the type2.lit service sends an initial stream header to type1.lit.

]]>

Next the type1.lit service sends a response stream header to type2.lit.

]]>

Because the type1.lit service does not support XMPP 1.0, it does not send stream features. Because the type2.lit service accepts verified connections, it attempts to verify the identity of type1.lit using server dialback. Therefore it sends a dialback key to type1.lit over the existing connection.

some-long-dialback-key
]]>

The type1.lit service then performs a DNS lookup on the type2.lit domain, opens a TCP connection at the discovered IP address and port, and establishes a stream with the authoritative server for the type2.lit service.

]]>

The authoritative server for the type2.lit service then returns a response stream header.

]]>

The type1.lit service then sends a dialback verification request to the authoritative server for the type2.lit domain.

some-long-dialback-key
]]>

Here we assume that the authoritative server for the type2.lit domain notifies the type1.lit service that the key is valid.

some-long-dialback-key
]]>

The type1.lit service then returns a positive server dialback result to the originating server (i.e., type2.lit).

some-long-dialback-key
]]>

Because the connection is successful, the type2.lit service routes the XML stanza from juliet@type2.lit to the type1.lit service.

In this scenario, an XMPP user juliet@type2.lit attempts to send an XML stanza to user@example.lit:

]]>

Therefore the type2.lit service (which accepts verified connections and has a self-signed certificate) attempts to initiate a server-to-server connection with the example.lit service (which also supports verified connections and has a self-signed certificate).

First, the type2.lit service sends an initial stream header to example.lit.

]]>

Next the example.lit service sends a response stream header to type2.lit.

]]>

Because the example.lit service supports XMPP 1.0, it also sends stream features.

]]>

We assume that type2.lit does not attempt STARTTLS negotiation but instead attempts server dialback for weak identity verification.

some-long-dialback-key
]]>

The example.lit service then performs a DNS lookup on the type2.lit domain, opens a TCP connection at the discovered IP address and port, and establishes a stream with the authoritative server for the type2.lit service.

]]>

The authoritative server for the type2.lit service then returns a response stream header.

]]>

The example.lit service then sends a dialback verification request to the authoritative server for the type2.lit domain.

some-long-dialback-key
]]>

Here we assume that the authoritative server for the type2.lit domain notifies the example.lit service that the key is valid.

some-long-dialback-key
]]>

The example.lit service then returns a positive server dialback result to the originating server (i.e., type2.lit).

some-long-dialback-key
]]>

Because the connection is successful, the type2.lit service routes the XML stanza from juliet@type2.lit to the example.lit service.

In this scenario, an XMPP user juliet@type2.lit attempts to send an XML stanza to romeo@type3.lit:

]]>

Therefore the type2.lit service (which accepts verified connections and has a self-signed certificate) attempts to initiate a server-to-server connection with the type3.lit service (which also supports verified connections and has a CA-issued certificate).

First, the type2.lit service sends an initial stream header to type3.lit.

]]>

Next the type3.lit service sends a response stream header to type2.lit.

]]>

Because the type3.lit service supports XMPP 1.0, it also sends stream features.

]]>

We assume that type2.lit does not attempt STARTTLS negotiation but instead attempts server dialback for weak identity verification.

some-long-dialback-key
]]>

The type3.lit service then performs a DNS lookup on the type2.lit domain, opens a TCP connection at the discovered IP address and port, and establishes a stream with the authoritative server for the type2.lit service.

]]>

The authoritative server for the type2.lit service then returns a response stream header.

]]>

The type3.lit service then sends a dialback verification request to the authoritative server for the type2.lit domain.

some-long-dialback-key
]]>

Here we assume that the authoritative server for the type2.lit domain notifies the type3.lit service that the key is valid.

some-long-dialback-key
]]>

The type3.lit service then returns a positive server dialback result to the originating server (i.e., type2.lit).

some-long-dialback-key
]]>

Because the connection is successful, the type2.lit service routes the XML stanza from juliet@type2.lit to the type3.lit service.

In this scenario, an XMPP user juliet@type2.lit attempts to send an XML stanza to hamlet@type4.lit:

]]>

Therefore the type2.lit service (which accepts verified connections and has a self-signed certificate) attempts to initiate a server-to-server connection with the type4.lit service (which also supports verified connections and has a CA-issued certificate).

First, the type2.lit service sends an initial stream header to type4.lit.

]]>

Next the type4.lit service sends a response stream header to type2.lit.

]]>

Because the type4.lit service supports XMPP 1.0, it also sends stream features.

]]>

Because type4.lit requires encryption, type2.lit attempts to negotiate a STARTTLS upgrade to the stream.

]]>
]]>

The servers then negotiate TLS. We assume the negotiation is successful.

The type2.lit service then opens a new stream over the encrypted connection.

]]>

Next the type4.lit service sends a response stream header to type2.lit.

]]>

Because the type4.lit service supports XMPP 1.0, it also sends stream features.

]]>

Notice that type4.lit requires dialback here (perhaps because of some local service policy). Therefore type2.lit sends a dialback key to type4.lit.

some-long-dialback-key
]]>

The type4.lit service then performs a DNS lookup on the type2.lit domain, opens a TCP connection at the discovered IP address and port, and establishes a stream with the authoritative server for the type2.lit service.

]]>

The authoritative server for the type2.lit service then returns a response stream header.

]]>

The type4.lit service then sends a dialback verification request to the authoritative server for the type2.lit domain.

some-long-dialback-key
]]>

Here we assume that the authoritative server for the type2.lit domain notifies the type4.lit service that the key is valid.

some-long-dialback-key
]]>

The type4.lit service then returns a positive server dialback result to the originating server (i.e., type2.lit).

some-long-dialback-key
]]>

Because the connection is successful, the type2.lit service routes the XML stanza from juliet@type2.lit to the type4.lit service.

In this scenario, an XMPP user juliet@type2.lit attempts to send an XML stanza to bill@type5.lit:

]]>

Therefore the type2.lit service (which accepts verified connections and has a self-signed certificate) attempts to initiate a server-to-server connection with the type5.lit service (which also supports verified connections and has a CA-issued certificate).

First, the type2.lit service sends an initial stream header to type5.lit.

]]>

Next the type5.lit service sends a response stream header to type2.lit.

]]>

Because the type5.lit service supports XMPP 1.0, it also sends stream features.

]]>

Because type5.lit requires encryption, type2.lit attempts to negotiate a STARTTLS upgrade to the stream.

]]>
]]>

The servers then negotiate TLS. We assume the negotiation is successful.

The type2.lit service then opens a new stream over the encrypted connection.

]]>

Next the type5.lit service sends a response stream header to type2.lit.

]]>

Because the type5.lit service supports XMPP 1.0, it also sends stream features.

]]>

Notice that type5.lit requires dialback here (perhaps because of some local service policy). Therefore type2.lit sends a dialback key to type5.lit.

some-long-dialback-key
]]>

The type5.lit service then performs a DNS lookup on the type2.lit domain, opens a TCP connection at the discovered IP address and port, and establishes a stream with the authoritative server for the type2.lit service.

]]>

The authoritative server for the type2.lit service then returns a response stream header.

]]>

The type5.lit service then sends a dialback verification request to the authoritative server for the type2.lit domain.

some-long-dialback-key
]]>

Here we assume that the authoritative server for the type2.lit domain notifies the type5.lit service that the key is valid.

some-long-dialback-key
]]>

The type5.lit service then returns a positive server dialback result to the originating server (i.e., type2.lit).

some-long-dialback-key
]]>

Because the connection is successful, the type2.lit service routes the XML stanza from juliet@type2.lit to the type5.lit service.

In this scenario, an XMPP user juliet@type2.lit attempts to send an XML stanza to chris@type6.lit.

]]>

Therefore the type2.lit service (which supports verified connections and has a self-signed certificate) attempts to initiate a server-to-server connection with the type6.lit service (which accepts only trusted connections, has a CA-issued certificate, and does not support Server Dialback).

First, the type2.lit service sends an initial stream header to type6.lit.

]]>

Next the type6.lit service sends a response stream header to type2.lit. Notice that the response stream header does not include the dialback namespace, since the type6.lit service does not support Server Dialback.

]]>

The type6.lit service also sends stream features. Because the type6.lit service does not accept untrusted connections, it returns stream features with a notation that STARTTLS is required.

]]>

Because type6.lit requires encryption, type2.lit attempts to negotiate a STARTTLS upgrade to the stream.

]]>
]]>

The servers then attempt negotiate TLS. We assume the negotiation fails because type2.lit presents a self-signed certificate but type6.lit requires trusted federation relying on a common root CA.

Because the connection is unsuccessful, the type2.lit service returns a stanza error to juliet@type2.lit, which should be &timeout;.

]]>

In this scenario, an XMPP user romeo@type3.lit attempts to send an XML stanza to citizen@type1.lit:

]]>

Therefore the type3.lit service (which accepts verified connections and has a CA-issued certificate) attempts to initiate a server-to-server connection with the type1.lit service (which supports verified connections only and does not have a certificate).

First, the type3.lit service sends an initial stream header to type1.lit.

]]>

Next the type1.lit service sends a response stream header to type3.lit.

]]>

Because the type1.lit service does not support XMPP 1.0, it does not send stream features. Therefore the type3.lit attempts to complete server dialback verification.

some-long-dialback-key
]]>

The type1.lit service then performs a DNS lookup on the type3.lit domain, opens a TCP connection at the discovered IP address and port, and establishes a stream with the authoritative server for the type3.lit service.

]]>

The authoritative server for the type3.lit service then returns a response stream header.

]]>

The type1.lit service then sends a dialback verification request to the authoritative server for the type3.lit domain.

some-long-dialback-key
]]>

Here we assume that the authoritative server for the type3.lit domain notifies the type1.lit service that the key is valid.

some-long-dialback-key
]]>

The type1.lit service then returns a positive server dialback result to the originating server (i.e., type3.lit).

some-long-dialback-key
]]>

Because the connection is successful, the type3.lit service routes the XML stanza from romeo@type3.lit to the type1.lit service.

In this scenario, an XMPP user romeo@type3.lit attempts to send an XML stanza to juliet@type2.lit:

]]>

Therefore the type3.lit service (which accepts verified connections and has a CA-issued certificate) attempts to initiate a server-to-server connection with the type2.lit service (which supports verified connections and has a self-signed certificate).

First, the type3.lit service sends an initial stream header to type2.lit.

]]>

Next the type2.lit service sends a response stream header to type3.lit.

]]>

Because the type3.lit service supports XMPP 1.0, it also sends stream features.

]]>

We assume that type2.lit does not attempt STARTTLS negotiation but instead attempts server dialback for weak identity verification.

some-long-dialback-key
]]>

The type2.lit service then performs a DNS lookup on the type3.lit domain, opens a TCP connection at the discovered IP address and port, and establishes a stream with the authoritative server for the type3.lit service.

]]>

The authoritative server for the type3.lit service then returns a response stream header.

]]>

The type2.lit service then sends a dialback verification request to the authoritative server for the type3.lit domain.

some-long-dialback-key
]]>

Here we assume that the authoritative server for the type3.lit domain notifies the type2.lit service that the key is valid.

some-long-dialback-key
]]>

The type2.lit service then returns a positive server dialback result to the originating server (i.e., type3.lit).

some-long-dialback-key
]]>

Because the connection is successful, the type3.lit service routes the XML stanza from romeo@type3.lit to the type2.lit service.

In this scenario, an XMPP user romeo@type3.lit attempts to send an XML stanza to user@example.lit:

]]>

Therefore the type3.lit service (which accepts verified connections and has a CA-issued certificate) attempts to initiate a server-to-server connection with the example.lit service (which also supports verified connections and has a CA-issued certificate).

First, the type3.lit service sends an initial stream header to example.lit.

]]>

Next the example.lit service sends a response stream header to type3.lit.

]]>

Because the type3.lit service supports XMPP 1.0, it also sends stream features.

]]>

We assume that example.lit does not attempt STARTTLS negotiation but instead attempts server dialback for weak identity verification.

some-long-dialback-key
]]>

The example.lit service then performs a DNS lookup on the type3.lit domain, opens a TCP connection at the discovered IP address and port, and establishes a stream with the authoritative server for the type3.lit service.

]]>

The authoritative server for the type3.lit service then returns a response stream header.

]]>

The example.lit service then sends a dialback verification request to the authoritative server for the type3.lit domain.

some-long-dialback-key
]]>

Here we assume that the authoritative server for the type3.lit domain notifies the example.lit service that the key is valid.

some-long-dialback-key
]]>

The example.lit service then returns a positive server dialback result to the originating server (i.e., type3.lit).

some-long-dialback-key
]]>

Because the connection is successful, the type3.lit service routes the XML stanza from romeo@type3.lit to the example.lit service.

In this scenario, an XMPP user romeo@type3.lit attempts to send an XML stanza to hamlet@type4.lit:

]]>

Therefore the type3.lit service (which accepts verified connections and has a CA-issued certificate) attempts to initiate a server-to-server connection with the type4.lit service (which also supports verified connections and has a CA-issued certificate).

First, the type3.lit service sends an initial stream header to type4.lit.

]]>

Next the type4.lit service sends a response stream header to type3.lit.

]]>

Because the type4.lit service supports XMPP 1.0, it also sends stream features.

]]>

Because type4.lit requires encryption, type3.lit attempts to negotiate a STARTTLS upgrade to the stream.

]]>
]]>

The servers then negotiate TLS. We assume the negotiation is successful.

The type3.lit service then opens a new stream over the encrypted connection.

]]>

Next the type4.lit service sends a response stream header to type3.lit.

]]>

Because the type4.lit service supports XMPP 1.0, it also sends stream features.

]]>

Notice that type4.lit requires dialback here (perhaps because of some local service policy). Therefore type3.lit sends a dialback key to type4.lit.

some-long-dialback-key
]]>

The type4.lit service then performs a DNS lookup on the type3.lit domain, opens a TCP connection at the discovered IP address and port, and establishes a stream with the authoritative server for the type3.lit service.

]]>

The authoritative server for the type3.lit service then returns a response stream header.

]]>

The type4.lit service then sends a dialback verification request to the authoritative server for the type3.lit domain.

some-long-dialback-key
]]>

Here we assume that the authoritative server for the type3.lit domain notifies the type4.lit service that the key is valid.

some-long-dialback-key
]]>

The type4.lit service then returns a positive server dialback result to the originating server (i.e., type3.lit).

some-long-dialback-key
]]>

Because the connection is successful, the type3.lit service routes the XML stanza from romeo@type3.lit to the type4.lit service.

In this scenario, an XMPP user romeo@type3.lit attempts to send an XML stanza to bill@type5.lit:

]]>

Therefore the type3.lit service (which accepts verified connections and has a CA-issued certificate) attempts to initiate a server-to-server connection with the type5.lit service (which also supports encrypted connections and has a CA-issued certificate).

First, the type3.lit service sends an initial stream header to type5.lit.

]]>

Next the type5.lit service sends a response stream header to type3.lit.

]]>

Because the type5.lit service supports XMPP 1.0, it also sends stream features.

]]>

Because type5.lit requires encryption, type3.lit attempts to negotiate a STARTTLS upgrade to the stream.

]]>
]]>

The servers then negotiate TLS. We assume the negotiation is successful.

The type3.lit service then opens a new stream over the encrypted connection.

]]>

Next the type5.lit service sends a response stream header to type3.lit.

]]>

Because the type5.lit service supports XMPP 1.0, it also sends stream features.

EXTERNAL
]]>

Notice that type5.lit requires use of SASL EXTERNAL here (because the certificate presented by type3.lit was issued by a common root CA). Therefore type3.lit attempts to complete SASL negotiation.

dHlwZTMubGl0
]]>

The type5.lit service determines that the authorization identity provided by type3.lit matches the information in the presented certificate and therefore returns success.

]]>

The type3.lit service then opens a new stream over the encrypted connection.

]]>

Next the type5.lit service sends a response stream header to type3.lit.

]]>

Because the type5.lit service supports XMPP 1.0, it also sends stream features (which in this case are empty).

]]>

Because the connection is successful, the type3.lit service routes the XML stanza from romeo@type3.lit to the type5.lit service.

In this scenario, an XMPP user romeo@type3.lit attempts to send an XML stanza to chris@type6.lit:

]]>

Therefore the type3.lit service (which accepts verified connections and has a CA-issued certificate) attempts to initiate a server-to-server connection with the type6.lit service (which requires trusted communications and has a CA-issued certificate).

First, the type3.lit service sends an initial stream header to type6.lit.

]]>

Next the type6.lit service sends a response stream header to type3.lit.

]]>

Because the type6.lit service supports XMPP 1.0, it also sends stream features.

]]>

Because type6.lit requires encryption, type3.lit attempts to negotiate a STARTTLS upgrade to the stream.

]]>
]]>

The servers then negotiate TLS. We assume the negotiation is successful.

The type3.lit service then opens a new stream over the encrypted connection.

]]>

Next the type6.lit service sends a response stream header to type3.lit.

]]>

Because the type6.lit service supports XMPP 1.0, it also sends stream features.

EXTERNAL
]]>

Notice that type6.lit requires use of SASL EXTERNAL here (because the certificate presented by type3.lit was issued by a common root CA). Therefore type3.lit attempts to complete SASL negotiation.

dHlwZTMubGl0
]]>

The type6.lit service determines that the authorization identity provided by type3.lit matches the information in the presented certificate and therefore returns success.

]]>

The type3.lit service then opens a new stream over the encrypted connection.

]]>

Next the type6.lit service sends a response stream header to type3.lit.

]]>

Because the type6.lit service supports XMPP 1.0, it also sends stream features (which in this case are empty).

]]>

Because the connection is successful, the type3.lit service routes the XML stanza from romeo@type3.lit to the type6.lit service.

In this scenario, an XMPP user hamlet@type4.lit attempts to send an XML stanza to citizen@type1.lit:

]]>

Therefore the type4.lit service (which requires encrypted connections and has a self-signed certificate) attempts to initiate a server-to-server connection with the type1.lit service (which supports verified connections only and does not have a certificate).

First, the type4.lit service sends an initial stream header to type1.lit.

]]>

Next the type1.lit service sends a response stream header to type4.lit.

]]>

Because the type1.lit service does not support XMPP 1.0, it does not send stream features. Because the type4.lit service requires encryption via TLS, it cannot proceed further with the stream negotiation and closes the stream.

]]>

The type1.lit service closes the stream as well.

]]>

Because the connection is unsuccessful, the type4.lit service returns a stanza error to hamlet@type4.lit, which should be &timeout;.

]]>

In this scenario, an XMPP user hamlet@type4.lit attempts to send an XML stanza to juliet@type2.lit:

]]>

Therefore the type4.lit service (which requires encrypted connections and has a self-signed certificate) attempts to initiate a server-to-server connection with the type2.lit service (which supports verified connections and has a self-signed certificate).

First, the type4.lit service sends an initial stream header to type2.lit.

]]>

Next the type2.lit service sends a response stream header to type4.lit.

]]>

Because the type2.lit service supports XMPP 1.0, it also sends stream features.

]]>

Because the type4.lit service requires encryption, it attempts STARTTLS negotiation.

]]>
]]>

The servers then negotiate TLS. We assume the negotiation is successful.

The type4.lit service then opens a new stream over the encrypted connection.

]]>

Next the type2.lit service sends a response stream header to type4.lit.

]]>

Because the type4.lit service supports XMPP 1.0, it also sends stream features.

]]>

Notice that type2.lit requires dialback here (perhaps because of some local service policy). Therefore type4.lit sends a dialback key to type2.lit.

some-long-dialback-key
]]>

The type2.lit service then performs a DNS lookup on the type4.lit domain, opens a TCP connection at the discovered IP address and port, and establishes a stream with the authoritative server for the type4.lit service.

]]>

The authoritative server for the type4.lit service then returns a response stream header.

]]>

The type2.lit service then sends a dialback verification request to the authoritative server for the type4.lit domain.

some-long-dialback-key
]]>

Here we assume that the authoritative server for the type4.lit domain notifies the type2.lit service that the key is valid.

some-long-dialback-key
]]>

The type2.lit service then returns a positive server dialback result to the originating server (i.e., type4.lit).

some-long-dialback-key
]]>

Because the connection is successful, the type4.lit service routes the XML stanza from hamlet@type4.lit to the type2.lit service.

In this scenario, an XMPP user hamlet@type4.lit attempts to send an XML stanza to romeo@type3.lit:

]]>

Therefore the type4.lit service (which requires encrypted connections and has a self-signed certificate) attempts to initiate a server-to-server connection with the type3.lit service (which supports verified connections and has a CA-issued certificate).

First, the type4.lit service sends an initial stream header to type3.lit.

]]>

Next the type3.lit service sends a response stream header to type4.lit.

]]>

Because the type3.lit service supports XMPP 1.0, it also sends stream features.

]]>

Because the type4.lit service requires encryption, it attempts STARTTLS negotiation.

]]>
]]>

The servers then negotiate TLS. We assume the negotiation is successful.

The type4.lit service then opens a new stream over the encrypted connection.

]]>

Next the type3.lit service sends a response stream header to type4.lit.

]]>

Because the type4.lit service supports XMPP 1.0, it also sends stream features.

]]>

Notice that type3.lit requires dialback here (perhaps because of some local service policy). Therefore type4.lit sends a dialback key to type3.lit.

some-long-dialback-key
]]>

The type3.lit service then performs a DNS lookup on the type4.lit domain, opens a TCP connection at the discovered IP address and port, and establishes a stream with the authoritative server for the type4.lit service.

]]>

The authoritative server for the type4.lit service then returns a response stream header.

]]>

The type3.lit service then sends a dialback verification request to the authoritative server for the type4.lit domain.

some-long-dialback-key
]]>

Here we assume that the authoritative server for the type4.lit domain notifies the type3.lit service that the key is valid.

some-long-dialback-key
]]>

The type3.lit service then returns a positive server dialback result to the originating server (i.e., type4.lit).

some-long-dialback-key
]]>

Because the connection is successful, the type4.lit service routes the XML stanza from hamlet@type4.lit to the type3.lit service.

In this scenario, an XMPP user hamlet@type4.lit attempts to send an XML stanza to user@example.lit:

]]>

Therefore the type4.lit service (which requires encrypted connections and has a self-signed certificate) attempts to initiate a server-to-server connection with the example.lit service (which also requires encrypted connections and has a self-signed certificate).

First, the type4.lit service sends an initial stream header to example.lit.

]]>

Next the example.lit service sends a response stream header to type4.lit.

]]>

Because the example.lit service supports XMPP 1.0, it also sends stream features.

]]>

Because the type4.lit service requires encryption, it attempts STARTTLS negotiation.

]]>
]]>

The servers then negotiate TLS. We assume the negotiation is successful.

The type4.lit service then opens a new stream over the encrypted connection.

]]>

Next the example.lit service sends a response stream header to type4.lit.

]]>

Because the type4.lit service supports XMPP 1.0, it also sends stream features.

]]>

Notice that example.lit requires dialback here (perhaps because of some local service policy). Therefore type4.lit sends a dialback key to example.lit.

some-long-dialback-key
]]>

The example.lit service then performs a DNS lookup on the type4.lit domain, opens a TCP connection at the discovered IP address and port, and establishes a stream with the authoritative server for the type4.lit service.

]]>

The authoritative server for the type4.lit service then returns a response stream header.

]]>

The example.lit service then sends a dialback verification request to the authoritative server for the type4.lit domain.

some-long-dialback-key
]]>

Here we assume that the authoritative server for the type4.lit domain notifies the example.lit service that the key is valid.

some-long-dialback-key
]]>

The example.lit service then returns a positive server dialback result to the originating server (i.e., type4.lit).

some-long-dialback-key
]]>

Because the connection is successful, the type4.lit service routes the XML stanza from hamlet@type4.lit to the example.lit service.

In this scenario, an XMPP user hamlet@type4.lit attempts to send an XML stanza to bill@type5.lit:

]]>

Therefore the type4.lit service (which requires encrypted connections and has a self-signed certificate) attempts to initiate a server-to-server connection with the type3.lit service (which also requires encrypted connections and has a CA-issued certificate).

First, the type4.lit service sends an initial stream header to type5.lit.

]]>

Next the type5.lit service sends a response stream header to type4.lit.

]]>

Because the type5.lit service supports XMPP 1.0, it also sends stream features.

]]>

Because the type4.lit service requires encryption, it attempts STARTTLS negotiation.

]]>
]]>

The servers then negotiate TLS. We assume the negotiation is successful.

The type4.lit service then opens a new stream over the encrypted connection.

]]>

Next the type5.lit service sends a response stream header to type4.lit.

]]>

Because the type4.lit service supports XMPP 1.0, it also sends stream features.

]]>

Notice that type5.lit requires dialback here (perhaps because of some local service policy). Therefore type4.lit sends a dialback key to type5.lit.

some-long-dialback-key
]]>

The type5.lit service then performs a DNS lookup on the type4.lit domain, opens a TCP connection at the discovered IP address and port, and establishes a stream with the authoritative server for the type4.lit service.

]]>

The authoritative server for the type4.lit service then returns a response stream header.

]]>

The type5.lit service then sends a dialback verification request to the authoritative server for the type4.lit domain.

some-long-dialback-key
]]>

Here we assume that the authoritative server for the type4.lit domain notifies the type5.lit service that the key is valid.

some-long-dialback-key
]]>

The type5.lit service then returns a positive server dialback result to the originating server (i.e., type4.lit).

some-long-dialback-key
]]>

Because the connection is successful, the type4.lit service routes the XML stanza from hamlet@type4.lit to the type5.lit service.

In this scenario, an XMPP user hamlet@type4.lit attempts to send an XML stanza to chris@type6.lit.

]]>

Therefore the type4.lit service (which requires encrypted connections and has a self-signed certificate) attempts to initiate a server-to-server connection with the type6.lit service (which accepts only trusted connections, has a CA-issued certificate, and does not support Server Dialback).

First, the type4.lit service sends an initial stream header to type6.lit.

]]>

Next the type6.lit service sends a response stream header to type4.lit. Notice that the response stream header does not include the dialback namespace, since the type6.lit service does not support Server Dialback.

]]>

The type6.lit service also sends stream features. Because the type6.lit service does not accept untrusted connections, it returns stream features with a notation that STARTTLS is required.

]]>

Because type6.lit requires encryption, type4.lit attempts to negotiate a STARTTLS upgrade to the stream.

]]>
]]>

The servers then attempt negotiate TLS. We assume the negotiation fails because type4.lit presents a self-signed certificate but type6.lit requires trusted federation relying on a common root CA.

Because the connection is unsuccessful, the type4.lit service returns a stanza error to hamlet@type4.lit, which should be &timeout;.

]]>

In this scenario, an XMPP user bill@type5.lit attempts to send an XML stanza to citizen@type1.lit:

]]>

Therefore the type5.lit service (which requires encrypted connections and has a CA-issued certificate) attempts to initiate a server-to-server connection with the type1.lit service (which supports verified connections only and does not have a certificate).

First, the type5.lit service sends an initial stream header to type1.lit.

]]>

Next the type1.lit service sends a response stream header to type5.lit.

]]>

Because the type1.lit service does not support XMPP 1.0, it does not send stream features. Because the type5.lit service requires encryption via TLS, it cannot proceed further with the stream negotiation and closes the stream.

]]>

The type1.lit service closes the stream as well.

]]>

Because the connection is unsuccessful, the type5.lit service returns a stanza error to hamlet@type5.lit, which should be &timeout;.

]]>

In this scenario, an XMPP user bill@type5.lit attempts to send an XML stanza to juliet@type2.lit:

]]>

Therefore the type5.lit service (which requires encrypted connections and has a CA-issued certificate) attempts to initiate a server-to-server connection with the type2.lit service (which supports verified connections and has a self-signed certificate).

First, the type5.lit service sends an initial stream header to type2.lit.

]]>

Next the type2.lit service sends a response stream header to type5.lit.

]]>

Because the type2.lit service supports XMPP 1.0, it also sends stream features.

]]>

Because the type5.lit service requires encryption, it attempts STARTTLS negotiation.

]]>
]]>

The servers then negotiate TLS. We assume the negotiation is successful.

The type5.lit service then opens a new stream over the encrypted connection.

]]>

Next the type2.lit service sends a response stream header to type5.lit.

]]>

Because the type5.lit service supports XMPP 1.0, it also sends stream features.

]]>

Notice that type2.lit requires dialback here (perhaps because of some local service policy). Therefore type5.lit sends a dialback key to type2.lit.

some-long-dialback-key
]]>

The type2.lit service then performs a DNS lookup on the type5.lit domain, opens a TCP connection at the discovered IP address and port, and establishes a stream with the authoritative server for the type5.lit service.

]]>

The authoritative server for the type5.lit service then returns a response stream header.

]]>

The type2.lit service then sends a dialback verification request to the authoritative server for the type5.lit domain.

some-long-dialback-key
]]>

Here we assume that the authoritative server for the type5.lit domain notifies the type2.lit service that the key is valid.

some-long-dialback-key
]]>

The type2.lit service then returns a positive server dialback result to the originating server (i.e., type5.lit).

some-long-dialback-key
]]>

Because the connection is successful, the type5.lit service routes the XML stanza from hamlet@type4.lit to the type2.lit service.

In this scenario, an XMPP user bill@type5.lit attempts to send an XML stanza to romeo@type3.lit:

]]>

Therefore the type5.lit service (which requires encrypted connections and has a CA-issued certificate) attempts to initiate a server-to-server connection with the type3.lit service (which accepts verified connections and has a CA-issued certificate).

First, the type5.lit service sends an initial stream header to type3.lit.

]]>

Next the type3.lit service sends a response stream header to type5.lit.

]]>

Because the type3.lit service supports XMPP 1.0, it also sends stream features.

]]>

Because type3.lit advertises encryption and type5.lit requires encryption, type5.lit attempts to negotiate a STARTTLS upgrade to the stream.

]]>
]]>

The servers then negotiate TLS. We assume the negotiation is successful.

The type5.lit service then opens a new stream over the encrypted connection.

]]>

Next the type3.lit service sends a response stream header to type5.lit.

]]>

Because the type3.lit service supports XMPP 1.0, it also sends stream features.

EXTERNAL
]]>

Notice that type3.lit requires use of SASL EXTERNAL here (because the certificate presented by type5.lit was issued by a common root CA). Therefore type5.lit attempts to complete SASL negotiation.

dHlwZTMubGl0
]]>

The type3.lit service determines that the authorization identity provided by type5.lit matches the information in the presented certificate and therefore returns success.

]]>

The type5.lit service then opens a new stream over the encrypted connection.

]]>

Next the type3.lit service sends a response stream header to type5.lit.

]]>

Because the type3.lit service supports XMPP 1.0, it also sends stream features (which in this case are empty).

]]>

Because the connection is successful, the type5.lit service routes the XML stanza from bill@type5.lit to the type3.lit service.

In this scenario, an XMPP user bill@type5.lit attempts to send an XML stanza to hamlet@type4.lit:

]]>

Therefore the type5.lit service (which requires encrypted connections and has a self-signed certificate) attempts to initiate a server-to-server connection with the type4.lit service (which also requires encrypted connections and has a self-signed certificate).

First, the type5.lit service sends an initial stream header to type4.lit.

]]>

Next the type4.lit service sends a response stream header to type5.lit.

]]>

Because the type4.lit service supports XMPP 1.0, it also sends stream features.

]]>

Because the type5.lit service requires encryption, it attempts STARTTLS negotiation.

]]>
]]>

The servers then negotiate TLS. We assume the negotiation is successful.

The type5.lit service then opens a new stream over the encrypted connection.

]]>

Next the type4.lit service sends a response stream header to type5.lit.

]]>

Because the type5.lit service supports XMPP 1.0, it also sends stream features.

]]>

Notice that type4.lit requires dialback here (perhaps because of some local service policy). Therefore type5.lit sends a dialback key to type4.lit.

some-long-dialback-key
]]>

The type4.lit service then performs a DNS lookup on the type5.lit domain, opens a TCP connection at the discovered IP address and port, and establishes a stream with the authoritative server for the type5.lit service.

]]>

The authoritative server for the type5.lit service then returns a response stream header.

]]>

The type4.lit service then sends a dialback verification request to the authoritative server for the type5.lit domain.

some-long-dialback-key
]]>

Here we assume that the authoritative server for the type5.lit domain notifies the type4.lit service that the key is valid.

some-long-dialback-key
]]>

The type4.lit service then returns a positive server dialback result to the originating server (i.e., type5.lit).

some-long-dialback-key
]]>

Because the connection is successful, the type5.lit service routes the XML stanza from hamlet@type4.lit to the type4.lit service.

In this scenario, an XMPP user bill@type5.lit attempts to send an XML stanza to user@example.lit:

]]>

Therefore the type5.lit service (which requires encrypted connections and has a CA-issued certificate) attempts to initiate a server-to-server connection with the example.lit service (which also requires encrypted connections and has a CA-issued certificate).

First, the type5.lit service sends an initial stream header to example.lit.

]]>

Next the example.lit service sends a response stream header to type5.lit.

]]>

Because the example.lit service supports XMPP 1.0, it also sends stream features.

]]>

Because both example.lit requires encryption and type5.lit also requires encryption, type5.lit attempts to negotiate a STARTTLS upgrade to the stream.

]]>
]]>

The servers then negotiate TLS. We assume the negotiation is successful.

The type5.lit service then opens a new stream over the encrypted connection.

]]>

Next the example.lit service sends a response stream header to type5.lit.

]]>

Because the example.lit service supports XMPP 1.0, it also sends stream features.

EXTERNAL
]]>

Notice that example.lit requires use of SASL EXTERNAL here (because the certificate presented by type5.lit was issued by a common root CA). Therefore type5.lit attempts to complete SASL negotiation.

dHlwZTMubGl0
]]>

The example.lit service determines that the authorization identity provided by type5.lit matches the information in the presented certificate and therefore returns success.

]]>

The type5.lit service then opens a new stream over the encrypted connection.

]]>

Next the example.lit service sends a response stream header to type5.lit.

]]>

Because the example.lit service supports XMPP 1.0, it also sends stream features (which in this case are empty).

]]>

Because the connection is successful, the type5.lit service routes the XML stanza from bill@type5.lit to the example.lit service.

In this scenario, an XMPP user bill@type5.lit attempts to send an XML stanza to chris@type6.lit:

]]>

Therefore the type5.lit service (which requires encrypted connections and has a CA-issued certificate) attempts to initiate a server-to-server connection with the type6.lit service (which requires trusted communications and has a CA-issued certificate).

First, the type5.lit service sends an initial stream header to type6.lit.

]]>

Next the type6.lit service sends a response stream header to type5.lit.

]]>

Because the type6.lit service supports XMPP 1.0, it also sends stream features.

]]>

Because type6.lit requires encryption, type5.lit attempts to negotiate a STARTTLS upgrade to the stream.

]]>
]]>

The servers then negotiate TLS. We assume the negotiation is successful.

The type5.lit service then opens a new stream over the encrypted connection.

]]>

Next the type6.lit service sends a response stream header to type5.lit.

]]>

Because the type6.lit service supports XMPP 1.0, it also sends stream features.

EXTERNAL
]]>

Notice that type6.lit requires use of SASL EXTERNAL here (because the certificate presented by type5.lit was issued by a common root CA). Therefore type5.lit attempts to complete SASL negotiation.

dHlwZTMubGl0
]]>

The type6.lit service determines that the authorization identity provided by type5.lit matches the information in the presented certificate and therefore returns success.

]]>

The type5.lit service then opens a new stream over the encrypted connection.

]]>

Next the type6.lit service sends a response stream header to type5.lit.

]]>

Because the type6.lit service supports XMPP 1.0, it also sends stream features (which in this case are empty).

]]>

Because the connection is successful, the type5.lit service routes the XML stanza from bill@type5.lit to the type6.lit service.

In this scenario, an XMPP user chris@type6.lit attempts to send an XML stanza to citizen@type1.lit:

]]>

Therefore the type6.lit service (which requires trusted connections and has a CA-issued certificate) attempts to initiate a server-to-server connection with the type1.lit service (which supports verified connections only and does not have a certificate).

First, the type6.lit service sends an initial stream header to type1.lit.

]]>

Next the type1.lit service sends a response stream header to type6.lit.

]]>

Because the type1.lit service does not support XMPP 1.0, it does not send stream features. Because the type6.lit service requires encryption via TLS, it cannot proceed further with the stream negotiation and closes the stream.

]]>

The type1.lit service closes the stream as well.

]]>

Because the connection is unsuccessful, the type6.lit service returns a stanza error to chris@type6.lit, which should be &timeout;.

]]>

In this scenario, an XMPP user chris@type6.lit attempts to send an XML stanza to juliet@type2.lit:

]]>

Therefore the type6.lit service (which requires encrypted connections and has a CA-issued certificate) attempts to initiate a server-to-server connection with the type2.lit service (which supports verified connections and has a self-signed certificate).

First, the type6.lit service sends an initial stream header to type2.lit.

]]>

Next the type2.lit service sends a response stream header to type6.lit.

]]>

Because the type2.lit service supports XMPP 1.0, it also sends stream features.

]]>

Because the type6.lit service requires encryption, it attempts STARTTLS negotiation.

]]>
]]>

The servers then attempt negotiate TLS. We assume the negotiation fails because type2.lit presents a self-signed certificate but type6.lit requires trusted federation relying on a common root CA.

Because the connection is unsuccessful, the type6.lit service returns a stanza error to chris@type6.lit, which should be &timeout;.

]]>

In this scenario, an XMPP user chris@type6.lit attempts to send an XML stanza to romeo@type3.lit:

]]>

Therefore the type6.lit service (which requires trusted connections and has a CA-issued certificate) attempts to initiate a server-to-server connection with the type3.lit service (which accepts verified connections and has a CA-issued certificate).

First, the type6.lit service sends an initial stream header to type3.lit.

]]>

Next the type3.lit service sends a response stream header to type6.lit.

]]>

Because the type3.lit service supports XMPP 1.0, it also sends stream features.

]]>

Because type3.lit advertises encryption and type6.lit requires encryption, type6.lit attempts to negotiate a STARTTLS upgrade to the stream.

]]>
]]>

The servers then negotiate TLS. We assume the negotiation is successful.

The type6.lit service then opens a new stream over the encrypted connection.

]]>

Next the type3.lit service sends a response stream header to type6.lit.

]]>

Because the type3.lit service supports XMPP 1.0, it also sends stream features.

EXTERNAL
]]>

Notice that type3.lit requires use of SASL EXTERNAL here (because the certificate presented by type6.lit was issued by a common root CA). Therefore type6.lit attempts to complete SASL negotiation.

dHlwZTMubGl0
]]>

The type3.lit service determines that the authorization identity provided by type6.lit matches the information in the presented certificate and therefore returns success.

]]>

The type6.lit service then opens a new stream over the encrypted connection.

]]>

Next the type3.lit service sends a response stream header to type6.lit.

]]>

Because the type3.lit service supports XMPP 1.0, it also sends stream features (which in this case are empty).

]]>

Because the connection is successful, the type6.lit service routes the XML stanza from chris@type6.lit to the type3.lit service.

In this scenario, an XMPP user chris@type6.lit attempts to send an XML stanza to hamlet@type4.lit:

]]>

Therefore the type6.lit service (which requires encrypted connections and has a CA-issued certificate) attempts to initiate a server-to-server connection with the type4.lit service (which supports verified connections and has a self-signed certificate).

First, the type6.lit service sends an initial stream header to type4.lit.

]]>

Next the type4.lit service sends a response stream header to type6.lit.

]]>

Because the type4.lit service supports XMPP 1.0, it also sends stream features.

]]>

Because the type6.lit service requires encryption, it attempts STARTTLS negotiation.

]]>
]]>

The servers then attempt negotiate TLS. We assume the negotiation fails because type4.lit presents a self-signed certificate but type6.lit requires trusted federation relying on a common root CA.

Because the connection is unsuccessful, the type6.lit service returns a stanza error to chris@type6.lit, which should be &timeout;.

]]>

In this scenario, an XMPP user chris@type6.lit attempts to send an XML stanza to bill@type5.lit:

]]>

Therefore the type6.lit service (which requires trusted connections and has a CA-issued certificate) attempts to initiate a server-to-server connection with the type5.lit service (which requires encrypted connections and has a CA-issued certificate).

First, the type6.lit service sends an initial stream header to type5.lit.

]]>

Next the type5.lit service sends a response stream header to type6.lit.

]]>

Because the type5.lit service supports XMPP 1.0, it also sends stream features.

]]>

Because type5.lit advertises encryption and type6.lit requires encryption, type6.lit attempts to negotiate a STARTTLS upgrade to the stream.

]]>
]]>

The servers then negotiate TLS. We assume the negotiation is successful.

The type6.lit service then opens a new stream over the encrypted connection.

]]>

Next the type5.lit service sends a response stream header to type6.lit.

]]>

Because the type5.lit service supports XMPP 1.0, it also sends stream features.

EXTERNAL
]]>

Notice that type5.lit requires use of SASL EXTERNAL here (because the certificate presented by type6.lit was issued by a common root CA). Therefore type6.lit attempts to complete SASL negotiation.

dHlwZTMubGl0
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The type5.lit service determines that the authorization identity provided by type6.lit matches the information in the presented certificate and therefore returns success.

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The type6.lit service then opens a new stream over the encrypted connection.

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Next the type5.lit service sends a response stream header to type6.lit.

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Because the type5.lit service supports XMPP 1.0, it also sends stream features (which in this case are empty).

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Because the connection is successful, the type6.lit service routes the XML stanza from chris@type6.lit to the type5.lit service.

In this scenario, an XMPP user chris@type6.lit attempts to send an XML stanza to user@example.lit:

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Therefore the type6.lit service (which requires trusted connections and has a CA-issued certificate) attempts to initiate a server-to-server connection with the example.lit service (which requires encrypted connections and has a CA-issued certificate).

First, the type6.lit service sends an initial stream header to example.lit.

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Next the example.lit service sends a response stream header to type6.lit.

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Because the example.lit service supports XMPP 1.0, it also sends stream features.

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Because example.lit advertises encryption and type6.lit requires encryption, type6.lit attempts to negotiate a STARTTLS upgrade to the stream.

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The servers then negotiate TLS. We assume the negotiation is successful.

The type6.lit service then opens a new stream over the encrypted connection.

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Next the example.lit service sends a response stream header to type6.lit.

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Because the example.lit service supports XMPP 1.0, it also sends stream features.

EXTERNAL
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Notice that example.lit requires use of SASL EXTERNAL here (because the certificate presented by type6.lit was issued by a common root CA). Therefore type6.lit attempts to complete SASL negotiation.

dHlwZTMubGl0
]]>

The example.lit service determines that the authorization identity provided by type6.lit matches the information in the presented certificate and therefore returns success.

]]>

The type6.lit service then opens a new stream over the encrypted connection.

]]>

Next the example.lit service sends a response stream header to type6.lit.

]]>

Because the example.lit service supports XMPP 1.0, it also sends stream features (which in this case are empty).

]]>

Because the connection is successful, the type6.lit service routes the XML stanza from chris@type6.lit to the example.lit service.

As explained in RFC 3920 and XEP-0220, Server Dialback does not provide authentication.

In the absence of out-of-band key exchange, acceptance of a self-signed certificate does not result in authentication of a peer and therefore should be followed by Server Dialback to weakly verify peer identity.

Acceptance of a certificate issued by a trusted root CA results in some level of authentication and therefore should be followed by SASL negotiation using the EXTERNAL mechanism.

This document requires no interaction with &IANA;.

This document requires no interaction with the &REGISTRAR;.

Thanks to Philipp Hancke, Norman Rasmussen, and Tomasz Sterna for their feedback.